Multi-stage isolation sub-system for a remote antenna unit

ABSTRACT

Certain features relate to a remote antenna unit having a multi-stage isolation sub-system for isolating uplink and downlink signal paths. A multi-stage isolation sub-system in the remote antenna unit can include a first stage device that is configured to generate a cancellation signal for canceling unwanted downlink signals received at the uplink antenna. The isolation sub-system can also include a second stage device configured to generate a cancellation signal that attenuates residual noise and intermodulation products generated in the downlink path and received in the uplink path. The multi-stage isolation sub-system can combine the cancellation signals with signals received on the uplink path in order to cancel or attenuate downlink leakage signals and residual noise present on the uplink path.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/114,624, filed Jul. 27, 2016 and titled MULTI-STAGE ISOLATIONSUB-SYSTEM FOR A REMOTE ANTENNA UNIT,” which claims priority to PCTApplication Serial No. PCT/US2015/012236, filed Jan. 21, 2015 and titled“MULTI-STAGE ISOLATION SUB-SYSTEM FOR A REMOTE ANTENNA UNIT,” whichclaims the benefit of U.S. Provisional Application Ser. No. 61/931,936,filed Jan. 27, 2014 and titled “A Multi-Stage Isolation Sub-System forRemote Antenna Unit,” the contents of all of which are herebyincorporated by reference.

TECHNICAL FIELD

The present disclosure relates generally to telecommunications systemsand more particularly (although not necessarily exclusively) to remoteantenna units in distributed antenna systems that can be configured toprovide enhanced signal isolation.

BACKGROUND

A distributed antenna system (“DAS”) can include one or more head-endunits and multiple remote antenna units coupled to each head-end unit. ADAS can be used to extend wireless coverage in an area. Head-end unitscan be connected to base stations. A head-end unit can receive downlinksignals from the base station and distribute downlink signals in analogor digital format to a radio frequency distribution system, which caninclude one or more remote antenna units. The remote antenna units cantransmit the downlink signals to user equipment devices within coverageareas serviced by the remote antenna units. In the uplink direction,signals from user equipment devices may be received by the remoteantenna units. The remote antenna units can transmit the uplink signalsreceived from user equipment devices to the head-end unit. The head-endunit can transmit uplink signals to the serving base stations.

Often, remote antenna units in a DAS can transmit and receive radiosignals simultaneously in multiple frequency bands. Simultaneouslytransmitting and receiving signals, however, can cause signal distortionin the uplink paths of the remote antenna units. For example, downlinksignals transmitted by a remote antenna unit or intermodulation productsof downlink signals may leak into an uplink signal path of the remoteantenna unit.

Remote antenna units can use a cavity filter for providing signalisolation between the transmit path and the receive path. Cavityfilters, however, can be large and expensive, and can therefore beundesirable in remote antenna units. Other options that may allow aremote antenna unit to avoid using a cavity filter include reducing theuplink or downlink power. Reducing the uplink or downlink power,however, undesirably limits the upper power of the telecommunicationsystem.

It is desirable to provide improved isolation between uplink anddownlink path in a remote antenna unit.

SUMMARY

According to one aspect, a multi-stage isolation sub-system is provided.The multi-stage isolation sub-system can include a first stage deviceand a second stage device that is communicatively coupled to the firststage device. The first stage device can include an air interfacemodeling module and is configured to generate a first cancellationsignal for attenuating a downlink leakage signal received on an uplinkchannel. The first cancellation signal can have an inverse phase ascompared to the downlink leakage signal. The second stage device caninclude a non-linearity modeling module and is configured to generate asecond cancellation signal for attenuating residual downlink noise anddownlink intermodulation products in a receiving frequency band.

According to another aspect, a method is provided. The method caninclude generating a first cancellation signal comprising an inversephase of a downlink leakage signal received on an uplink channel basedon an air interface model. The method can also include generating asecond cancellation signal for attenuating residual downlink noise anddownlink intermodulation products received on the uplink channel basedon a non-linearity model. The method can further include attenuating thedownlink leakage signal by combining the first cancellation signal withsignals received on the uplink channel and attenuating the residualdownlink noise and downlink intermodulation products by combining thesecond cancellation signal with the signals received on the uplinkchannel.

According to another aspect, a remote antenna unit is provided. Theremote antenna unit can include a multi-stage isolation sub-systemcommunicatively coupled to an uplink antenna and a downlink antenna. Themulti-stage isolation sub-system can include a first stage deviceconfigured to generate a first cancellation signal. The firstcancellation signal can have an inverse phase as compared to a downlinkleakage signal received at the uplink antenna. The multi-stage isolationsub-system can also include a second stage device communicativelycoupled to the first stage device. The second stage device can include anon-linearity modeling module and can be configured to generate a secondcancellation signal to attenuate residual downlink noise and downlinkintermodulation products received at the uplink antenna.

These illustrative aspects and features are mentioned not to limit ordefine the disclosure, but to provide examples to aid understanding ofthe concepts disclosed in this application. Other aspects, advantages,and features of the present disclosure will become apparent after reviewof the entire application.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an example of a base station and a distributed antennasystem comprising remote antenna units that can be configured forenhanced signal isolation according to one aspect of the presentdisclosure.

FIG. 2 is a block diagram depicting an example of a multi-stageisolation sub-system in a remote antenna unit according to one aspect ofthe present disclosure.

FIG. 3 is a block diagram depicting an alternative example of amulti-stage isolation sub-system in a remote antenna unit according toone aspect of the present disclosure.

FIG. 4 is a block diagram depicting another example of a multi-stageisolation sub-system in a remote antenna unit according to one aspect ofthe present disclosure.

FIG. 5 is a flowchart depicting a process for using a multi-stageisolation sub-system in a remote antenna unit according to one aspect ofthe present disclosure.

DETAILED DESCRIPTION

Certain aspects and features relate to a multi-stage isolationsub-system for a remote antenna unit in a telecommunication system. Themulti-stage isolation sub-system can provide signal isolation betweenuplink and downlink signal paths in the remote antenna unit by modelingthe air interface between the uplink and downlink paths and using theair interface model to generate cancellation signals. In some aspects, acancellation signal can be a signal having an inverse phase incomparison to another signal. The cancellation signals can reduce oreliminate different types of distortions received in the uplink path ofa remote antenna unit. The cancellation signal can be generated byinverting one or more signal components of a signal, including (but notlimited to) the phase of the signal. For example, the cancellationsignal can include both phase and frequency components that are inverseof the phase and frequency of unwanted signal components.

According to certain aspects, a first stage device in a multi-stageisolation sub-system can generate a cancellation signal that can be usedfor cancelling or attenuating downlink leakage signals that can bereceived by the uplink antenna of the remote antenna unit. The downlinkleakage can depend on various environmental factors (e.g., the roomdimensions, whether people are moving nearby, whether doors are movingor not). As a result, the leakage channel between the downlink anduplink can slowly change over time. The multi-stage isolation sub-systemcan model this time-varying channel using a reference signal for thedownlink signals that are received at the uplink antenna ports. As usedherein, a “reference signal” may refer to the signal used to generatethe cancellation signal that can attenuate the downlink leakage on theuplink path. The reference signal can be obtained by filtering theuplink signal with a filter having a passband at the downlink frequencyband. The phase of the cancellation signal can be inverse (i.e.,opposite) to the phase of the reference signal. For example, if thephase difference between the cancellation signal and the referencesignal is 180 degrees, then the phase of the cancellation signal isinverse to the phase of the reference signal. By combining the signalsreceived on the uplink transmission path with the generated cancellationsignal, the leaked downlink components on the uplink path can becanceled or attenuated.

A second stage device in the multi-stage isolation sub-system cangenerate a cancellation signal that can be used for attenuatingadditional residual noise or intermodulation products generated in thedownlink path and received in the uplink path. The residual noise orintermodulation products can thereby be removed from uplink signalstraversing the uplink path of the remote antenna unit. The referencesignal used to generate a cancellation signal for attenuating additionalresidual noise can be obtained by filtering the uplink signal with afilter having a passband at the uplink frequency band.

It is appreciated that perfect cancellation of the downlink leakagesignal and residual noise and intermodulation products may not berequired. For example, additional isolation between the uplink anddownlink paths can be achieved by reducing the downlink signal power by20-30 dB.

The multi-stage isolation sub-system described herein can increase theisolation between the uplink and downlink signals such that the downlinkoutput power can be increased while minimizing interference at the inputto a low-noise amplifier following the uplink antenna. Further, amulti-stage isolation sub-system can provide a more flexible solutionthan remote antenna units that uses cavity filters to provide antennaisolation. For example, the remote antenna unit described herein can beconfigured to transmit using a greater variety of power levels orutilize smaller antennas with less isolation. A multi-stage isolationsub-system can also provide a solution in which no cavity filtering isrequired to provide antenna isolation.

In some aspects, the remote antenna unit can be configured for frequencydivision duplexing (“FDD”) operation. In other aspects, the remoteantenna unit can be configured for time division duplexing (“TDD”)operation. In additional or alternative aspects, the remote antenna unitcan be configured for both FDD and TDD operation. Simultaneous supportfor multiple unsynchronized TDD systems (e.g., Wi-Fi) or joint operationof TDD and FDD may be beneficial (e.g., LTE-FDD/TD-LTE operation in band7/band 38).

Detailed descriptions of certain examples are discussed below. Theseillustrative examples are given to introduce the reader to the generalsubject matter discussed here and are not intended to limit the scope ofthe disclosed concepts. The following sections describe variousadditional aspects and examples with reference to the drawings in whichlike numerals indicate like elements, and directional descriptions areused to describe the illustrative examples but, like the illustrativeexamples, should not be used to limit the present disclosure.

FIG. 1 depicts an example of a distributed antenna system (“DAS”) 100that includes a network of spatially separated remote antenna units 104a-f coupled to a head-end unit 102. The remote antenna units 104 a-f canbe communicatively coupled to a common signal source, such as thehead-end unit 102, for communicating with a base station 114. In oneaspect the remote antenna units 104 a-f can be coupled directly to thehead-end unit 102. In other aspects, the remote antenna units 104 a-fcan be coupled to the head-end unit 102 via a distribution andaggregation network 106 comprising one or more splitter units 108,combiner units 110, and a transport network including transportationmedia for communicatively coupling components of the distribution andaggregation network 106 that are distributed over a building or otherarea serviced by the DAS 100.

The head-end unit 102 can receive downlink signals from one or more basestations 114 and transmit uplink signals to the base station 114. Anysuitable communication link can be used for communication between thebase station 114 and the head-end unit 102, such as (but not limited to)a direct connection or a wireless connection. A direct connection caninclude, for example, a connection via a copper, optical fiber, or othersuitable communication medium. The head-end unit 102 can transmitdownlink signals to the remote antenna units 104 a-f and receive uplinksignals from the remote antenna units 104 a-f. Any suitablecommunication link can be used for communication between the head-endunit 102 and remote antenna units 104 a-f, such as (but not limited to)a direct connection or a wireless connection.

The distribution and aggregation network 106 can be a passive radiodistribution network for splitting and combining signals between thehead-end unit 102 and the remote antenna units 102 a-f. For example, thesplitter units 108 may split downlink signals received from a basestation 114 for transmission to multiple remote antenna units and thecombiner units 110 may combine uplink signals received from the remoteantenna units 104 a-f for transmission to the head-end unit 102.

The remote antenna units 104 a-f can provide signal coverage in coveragezones 112 a-c by transmitting downlink signals to mobile communicationdevices or other user equipment in the coverage zones 112 a-c andreceiving uplink signals from the mobile communication devices or otheruser equipment in the coverage zones 112 a-c. The remote antenna units104 a-f can transmit uplink signals to the head-end unit 102 or otherunit. The head-end unit 102 or other unit can combine uplink signalsreceived from remote antenna units 104 a-f for transmission to the basestation 114.

The remote antenna units 104 a-f can include multi-stage isolationsub-systems 150, 152, 154, 156, 158, and 160, respectively, forattenuating downlink leakage signals and residual noise received on theuplink antennas of the remote antenna units 104 a-f. In some aspects,remote antenna units 104 a-f may support multi-band operation andinclude multiple sets of transmit and receive antennas, each set oftransmit and receive antennas supporting different frequency bands.Remote antenna units 104 a-f with multiple sets of transmit and receiveantennas can include multiple multi-stage isolation sub-systems. FIGS.2-4 depict examples of certain configurations of a multi-stage isolationsub-system.

FIG. 2 depicts an example of a multi-stage isolation sub-system 150 of aremote antenna unit 104 a. The remote antenna unit 104 a transmitsdownlink signals on a downlink antenna 226 and receives uplink signalson an uplink antenna 224. Downlink signals transmitted by the downlinkantenna 226 can leak into the uplink antenna 224. The multi-stageisolation sub-system 150 can reduce this unwanted leakage via a digitalprocessing module 202 communicatively coupled to an integrated radiodevice 204. Although the term “integrated radio device” is used anddepicted in FIG. 2, other implementations are possible. For example, insome aspects, the integrated radio device 204 can be replaced with orsupplemented by any discrete device or multiple discrete devices thatperform the functionality of the integrated radio device 204 asdescribed herein.

The integrated radio device 204 can operate as the interface between theuplink antenna 224 and the downlink antenna 226 (which respectivelyreceive and transmit analog RF waveforms) and the digital processingmodule 202 (which can process binary information formatted in digitalsequences of 1s and 0s). The integrated radio device 204 may include anbroadband receive chain 218 and two downlink signal processing chains220 a-b. The term “broadband” can refer to the capability to transmitand receive multiple frequency bands. The broadband receive chain 218can be positioned in an uplink path and can include down-conversioncircuitry. Each of the downlink signal processing chains 220 a-b caninclude up-conversion circuitry. Each of the broadband receive chain 218and the downlink signal processing chains 220 a-b can be communicativelycoupled to local oscillators 222, 246. The local oscillators 222, 246can generate a signal that is used for up-conversion of downlink signalsand down-conversion of uplink signals. In some aspects, the localoscillators 222, 246 can be shared between the broadband receive chain218 and the downlink signal processing chains 220 a-b. Further, whiletwo local oscillators 222, 246 are shown for illustrative purposes, itis understood that in other aspects, each processing chain may beassociated with an individual local oscillator. In other aspects, theintegrated radio device 204 may not include the downlink signalprocessing chain 220 a.

The broadband receive chain 218 can be included in or communicativelycoupled to the uplink path. The broadband receive chain 218 can becommunicatively coupled to the uplink antenna 224 and a low-noiseamplifier 228. The low-noise amplifier 228 can amplify signals receivedvia the uplink antenna 224. The broadband receive chain 218 can convertthe uplink analog RF waveform to a digital signal for input to thedigital processing module 202. The uplink antenna 224 may also becommunicatively coupled to the downlink signal processing chain 220 avia a reference path 242 between the uplink and downlink paths. Thedownlink signal processing chain 220 b can be communicatively coupled tothe downlink antenna 226. The downlink signal processing chain 220 b canconvert downlink digital signals received from the digital processingmodule 202 to downlink analog RF waveforms for transmission.

The digital processing module 202 can model an air interface channelthat exists between the uplink antenna 224 and the downlink antenna 226.The digital processing module 202 can use the air interface model togenerate a first cancellation signal 230 that can cancel or otherwiseattenuate leaked downlink signals traversing the uplink path. Thedigital processing module 202 can also generate a second cancellationsignal 232 that can be used for cancelling signal components resultingfrom non-linearities in the uplink and downlink path (e.g.,intermodulation products), downlink interference resulting from noisegenerated by components in the downlink path, and downlink interferencegenerated by variations in the air interface between the downlinkantenna 226 and the uplink antenna 224.

The digital processing module 202 can be implemented using any suitableprocessing device that can process digital signals (i.e., signalscarrying information formatted as binary sequences of 1s and 0s).Non-limiting examples of suitable processing devices include afield-programmable gate array (“FPGA”), a microprocessor, a peripheralinterface controller (“PIC”), an application-specific integrated circuit(“ASIC”), or other suitable processor. The particular hardware used toimplement the subject matter described herein may depend on the desiredadaptation speed. For example, the adaptation algorithm may beimplemented using a microprocessor (very slow), a digital signalprocessor (DSP) (slow) or FPGA/vector processor (fast).

The first cancellation signal 230 can be generated in the digitalprocessing module 202 using an adaptive filter 214 communicativelycoupled to an air interface modeling module 212. Downlink signals thatleak into the uplink signal path can be sampled from the uplink path.The sampled signal can be provided to the air interface modeling module212 as a reference signal 240. Using the reference signal 240, the airinterface modeling module 212 can model the air interface that existsbetween the downlink antenna 226 and the uplink antenna 224 and generateparameters to control the adaptive filter 214. The air interfacemodeling module 212 can generate parameters of the air interface using,for example, a least means square (“LMS”) filter approach, Wienerfilter, zero forcing equalizer, or kernel filters. For example, an LMSalgorithm including the formula e(n)=(y(n)+v(n))−ŷ(n) can be used tomodel the air interface. The air interface can correspond to the unknownsystem y(n) in the LMS algorithm. The uplink signal can be filteredusing a filter having a passband at the downlink frequency band. Thefiltered uplink signal can correspond to the ŷ(n) term in the LMSalgorithm. Non-linearities in the downlink signal processing chain andthe LNA can correspond to interference v(n) in the LMS algorithm. Thereference signal can correspond to an error signal e(n) in the LMSalgorithm. Based on the LMS algorithm, the air interface y(n) can bedetermined from the interference v(n) (i.e., the non-linearities in thedownlink signal processing chain and the LNA), the error signal e(n)(i.e., the reference signal), and the filtered input signal ŷ(n) (i.e.the filtered uplink signal). The parameters generated by the airinterface modeling module 212 can include information indicating theamount of amplitude adjustment required to match the leakage downlinksignal received at the uplink signal. The parameters can also includeinformation indicating the amount of phase shift to apply in order togenerate a signal with an opposite phase to the downlink leakage signal.In other aspects, more complex air interfaces can be modeled. Forexample, the air interface modeling module 212 can generate parametersthat take into account several signal reflection paths.

The parameters generated by the air interface modeling module 212 can beprovided to the adaptive filter 214. The adaptive filter 214 can use thereceived parameters to process the amplitude and phase of the downlinksignal to generate the first cancellation signal 230. The firstcancellation signal 230 can be provided from the adaptive filter 214 tothe downlink signal processing chain 220 a in the integrated radiodevice 204 for up-conversion to an RF frequency and digital-to-analogconversion. After processing in the integrated radio device 204, thefirst cancellation signal 230 can be coupled to the uplink path via acoupler 234 at a point before the low-noise amplifier 228. As usedherein, a coupler can include a standard power combiner or other devicethat can combine two radio frequency signals. In aspects where thedownlink signal processing chain 220 a is not included in the integratedradio device 204, multi-stage isolation sub-system may not include thecoupler 234.

To generate the second cancellation signal 232, the reference signal 240can be sampled from the downlink leakage signal on the uplink path andprovided to a non-linearity modeling module 210. The non-linearitymodeling module 210 can process the reference signal 240 to model theeffects of non-linearities in the downlink and uplink paths. Effects ofnon-linearities in the downlink and uplink paths can include distortionscaused by the downlink signal in the uplink frequency band. Models ofthe effects of non-linearities in the downlink and uplink paths can beused to generate the second cancellation signal 232 to compensate forthe non-linearities. Non-linearities in the downlink and uplink pathscan be modeled using similar techniques to that of digitalpre-distortion of amplifiers. The non-linearities model can be used tocompensate for non-linearities in the downlink signal processing chain,the LNA and the uplink signal processing chain. Using thenon-linearities model can minimize the distortions caused by thedownlink signal in the uplink frequency band. A mathematical modelcorresponding to distortion caused by non-linearities can be determinedbased on hardware characteristics of the devices in the downlink signalprocessing chain and/or interconnections between devices in the chain,the LNA, and the devices in the uplink signal processing chain and/orinterconnections between devices in the chain. The mathematical modelcan also correspond to distortion caused by non-linearities in the airinterface. In additional or alternative aspects, one or more signalpaths can be modeled as one or more Volterra filter stages to obtain anon-linearities model.

Based on the non-linearity model, the non-linearity modeling module 210can generate parameters to control a non-linear equalizer 208 that iscommunicatively coupled to the non-linearity modeling module 210 and thedownlink path. The parameters from the non-linearity modeling module 210can indicate the amount of phase shift to apply to the downlink signalin order to generate a signal with an inverse phase with any residualnoise and intermodulation byproducts. The non-linear equalizer 208(which can be implemented as a higher order equalizer) can modify thedownlink signal to create the second cancellation signal 232 to cancelresidual intermodulation products in the uplink path. The secondcancellation signal 232 can be combined with digital signals on theuplink path at a point before the uplink filter 206 using a summationdevice 238. Delay units 244, 248 can be used to compensate for theprocessing delay caused by the adaptive filter 214 and the non-linearequalizer 208.

In some aspects, one or more of the uplink filter 206, the non-linearequalizer 208, the non-linearity modeling module 210, the air interfacemodeling module 212, and an adaptive filter 214 can be implemented assoftware modules executed by a processing device. In additional oralternative aspects, one or more of the uplink filter 206, thenon-linear equalizer 208, the non-linearity modeling module 210, the airinterface modeling module 212, and the adaptive filter 214 can beimplemented using suitable hardware devices such as an FPGA or a vectorprocessor.

In other aspects, the non-linear equalizer 208 can be implemented as ahigher order equalizer including a finite impulse response (“FIR”)filter. The air interface modeling module 212 can model air interfaceparameters as FIR coefficients that are calculated using amicroprocessor or other suitable processing device. The parameters ofthe air interface model can be fed into an adaptive filter implementedas a FIR filter on an FPGA processor or other suitable processingdevice. The FIR filter can correspond to an air interface radio channel.The non-linearity modeling module 210 can model parameters as FIRcoefficients for Volterra stages. The FIR coefficients can be calculatedon a microprocessor or other suitable processing device. The parameterscan be fed into a Volterra model on the a microprocessor or othersuitable processing device.

FIG. 3 depicts an alternative example of a multi-stage isolationsub-system 150′ of remote antenna unit 104 a′. Similar to the systemdepicted in FIG. 2, the multi-stage isolation sub-system 150′ depictedin FIG. 3 can model the air interface channel between the uplink anddownlink path and also model non-linearities that may exist in the airinterface or the LNA 318. The air interface model can be used togenerate a first cancellation signal 320 to cancel or attenuate downlinkleakage signals received by the uplink antenna 314. The model fornon-linearities can be used to generate a second cancellation signal 322that can cancel or attenuate the additional non-linearities by the LNA318, The second cancellation signal 322 can also attenuate non-linearcomponents of a downlink signal processing chain 304 by minimizing thepower in the receive band. A noise contribution from the transmitterchain in the receive band may be uncorrelated with a desired signal thathas been received.

The multi-stage isolation sub-system 150′ includes a dual channelprocessor 300. A non-limiting example of a dual channel processor is aScintera SC2200. The dual channel processor 300 is communicativelycoupled to the downlink path via a coupler 330 and is communicativelycoupled to multiple points in the uplink path via couplers 332, 334,336. A downlink signal, after being processed in the downlink signalprocessing chain 304, is provided to a sampling receiver 302 andnon-linear equalizers 310,316. The downlink signal provided from coupler330 can be used as a reference signal 348 for the downlink path. Thesampling receiver 302 also receives a second reference signal 346 forthe downlink leakage signal received at the uplink channel. The coupler336 can communicatively couple the sampling receiver 302 to the uplinkpath. The coupler 336 can capture both the uplink and downlink frequencybands. The sampling receiver 302 can include any suitable broadbandreceiver with a capture unit. The sampling receiver 302 iscommunicatively coupled to a non-linearity modeling module 306 and airinterface modeling module 308. The reference signal 348 received via thecoupler 330 can be used to adapt the first stage of the multi-stageisolation subsystem 150′, and the second reference signal 346 can beused to adapt the second stage of the multi-stage isolation sub-system150′.

Using the reference signal 346, the air interface modeling module 308models the air interface between the uplink channel and the downlinkchannel. The air interface modeling module 308 uses the air interfacemodel to calculate an amount of phase shift to apply to the direct pathof the received uplink signals to attenuate downlink leakage signals. Inother aspects, the air interface modeling module 308 can use the airinterface model to calculate parameters for a higher order filter inorder to attenuate downlink leakage signals from reflected RF paths. Theair interface modeling module 308 provides parameters for controllingthe non-linear equalizer 310. For example, the air interface modelingmodule 308 can provide parameters that can include the amount of phaseshift and the amount of amplitude shift per direct or reflected radiopath to apply in order to match the inverse phase of the downlinkleakage signal. The non-linear equalizer 310 uses the parameters fromthe air interface modeling module 308 to generate the first cancellationsignal 320. The first cancellation signal 320 can be combined withsignals on the uplink path at a point before a low-noise amplifier 318using the coupler 332, thereby canceling or attenuating the downlinkleakage signals traversing the uplink path.

Using the reference signal 346, the non-linearity modeling module 306models the residual noise and non-linearities of the LNA 318 between theuplink path and the downlink path. The non-linearity modeling module 306provides parameters identifying the amount of phase shift to apply tothe uplink signal to attenuate the residual noise and intermodulationproducts to the non-linear equalizer 316. The non-linear analogequalizer 316 uses the parameters received from the non-linearitymodeling module 306 to provide the second cancellation signal 322. Thesecond cancellation signal 322 may be outputted by the non-linear analogequalizer 316 and coupled to the uplink path after the low-noiseamplifier 318. The uplink path signal, after being processed by thefirst cancellation signal 320 and the second cancellation signal 322,may be provided back into the sampling receiver 302 or provided to anuplink signal processing chain 324 for uplink signal processing.

FIG. 4 depicts another example of a block diagram for a multi-stageisolation sub-system 150″ of remote antenna unit 104(a)″. Similar to thesystems depicted in FIGS. 2 and 3, the multi-stage isolation sub-system150″ can model the air interface channel between the uplink and downlinkpath as well as the non-linearities that may exist in the LNA 416 andthe air interface. The air interface model can be used to generate afirst cancellation signal 414 to cancel or attenuate downlink leakagesignals received on the uplink path. In some aspects, the air interfacemodel can focus on the direct RF path between the uplink antenna 450 andthe downlink antenna 452. The model for non-linearities can be used togenerate a second cancellation signal 418 that can cancel or attenuatethe additional non-linearities in the downlink path and the uplink path.

The isolation sub-system 150″ can include a single channelmicroprocessor 400. A non-limiting example of a single channelmicroprocessor 400 is a Scintera SC1894. The single channelmicroprocessor 400 is communicatively coupled to the downlink path via acoupler 430 and communicatively coupled to multiple points in the uplinkpath via couplers 432, 434, 440. A downlink signal, after beingprocessed by a downlink signal processing chain 436, can be sampled fromthe downlink path via the coupler 430. The sampled signal can beprovided to the single channel microprocessor 400 and a variable gainmodule 410. The sampled signal can be provided to a sampling receiver402 and a non-linear equalizer 406 of the single channel microprocessor400. Downlink signals that leak into the uplink path can be sampled viathe coupler 440. The sampled downlink leakage signal can be provided tothe sampling receiver 402 as a reference signal 438.

The sampling receiver 402 in the single channel microprocessor 400 canbe communicatively coupled to a non-linearity modeling module 404 and again/phase control module 408. Parameters generated by the non-linearequalizer 406 can be provided to the gain/phase control module 408. Thegain/phase control module 408 can drive the variable phase unit 412 andthe variable gain unit 410 to adjust the phase and amplitude of thereceived signal and thus attenuate the downlink leakage signal receivedat the uplink antenna 450. Adjusting the phase of the incoming signalcan also accommodate for any delay and signal loss due to antennacoupling.

The sampling receiver 402 is also communicatively coupled to anon-linearity modeling module 404. The non-linearity modeling module 404can generate parameters for controlling the non-linear equalizer 406.Similar to FIGS. 2-3, the parameters generated by the non-linearitymodeling module 404 can include an amplitude adjustment and amount ofphase shift to apply in order to attenuate downlink noise andintermodulation products. Based on the parameters from the non-linearitymodeling module 404, the non-linear equalizer 406 can generate thesecond cancellation signal 418. The second cancellation signal 418 canbe coupled to the uplink path at a point before a low-noise amplifier416. The attenuated signal can be further processed by an uplink signalprocessing chain 420 for uplink signal processing.

FIG. 5 is a flow chart depicting an example of a process for using amulti-stage isolation sub-system in a remote antenna unit according toone aspect of the present disclosure. The process is described withrespect to the system depicted in FIG. 1. Other implementations,however, are possible.

In block 500, a multi-stage isolation sub-system of a remote antennaunit generates, based on an air interface model, a first cancellationsignal comprising an inverse phase of a downlink leakage signal receivedon an uplink channel. In some aspects, the cancellation signal caninclude an inverse phase of the downlink leakage signal. In additionalor alternative aspects, the cancellation signal can include one or moreother inverse signal characteristics of the downlink leakage signal. Forexample, in an air interface channel, a phase of a signal may be relatedto a frequency of the signal and an attenuation of a signal may berelated to the frequency of the signal. One or more of these signalcharacteristics may be inverted to obtain an inverted channel. Unwantedbroadband transmit signal components in a receive path may pass theinverted channel and thereby result in an inverted signal used forcancellation. In a non-limiting example, the multi-stage isolationsub-system can include an air interface modeling module 212 or 308 forgenerating an air interface model from a sampled reference signal. Themulti-stage isolation sub-system can also include a digital processingmodule 202 with an adaptive filter 214 for generating the firstcancellation signal based on the air interface model and an integratedradio device 204 for interfacing the digital processing module 202 tothe RF antennas. In another example, the multi-stage isolationsub-system can include a dual channel processor with a first non-linearequalizer 310 that can generate the first cancellation signal. In afurther example, the multi-stage isolation sub-system can include again/phase control module 408 for generating the first cancellationsignal.

The first cancellation signal can be generated using the techniquesdescribed above with respect to FIGS. 2-4. For example, the downlinkleakage signal can be provided to the multi-stage isolation sub-systemvia a reference signal. The multi-stage isolation sub-system can use thereference signal to model the air interface between the uplink antennaand the downlink antenna and generate parameters indicating the amountof phase shift to apply to the uplink signal to cancel the downlinkleakage signal.

In block 502, a multi-stage isolation sub-system can generate, based ona non-linearity model, a second cancellation signal for attenuatingresidual downlink noise and downlink intermodulation products receivedon the uplink channel. In a non-limiting example, the multi-stageisolation sub-system can include one of the non-linear modeling modules210, 306, or 404 that can model the non-linearities and residual noisepresent in the air interface between the uplink and downlink antennas.The multi-stage isolation sub-system can also include one of thenon-linear equalizers 208, 316, or 406 that can generate the secondcancellation signal based on the non-linearity model. The secondcancellation signal can be generated using the techniques described withrespect to FIGS. 2-4. For example, the non-linearity modeling module canuse the non-linearity model to generate parameters indicating the amountof phase shift to apply in order to generate the second cancellationsignal.

In block 504, a multi-stage isolation sub-system can attenuate thedownlink leakage signal by combining the first cancellation signal withsignals received on the uplink channel. For example, the multi-stageisolation sub-system can combine the signals received on the uplinkchannel with the first cancellation signal with a standard RF couplerdevice, such as a directional coupler. A directional coupler can combinethe power of two RF signals that contain the same frequency. As thefirst cancellation signal has a phase inverse to that of the downlinkleakage signal, combining the first cancellation signal with signals onthe uplink channel can result in attenuating or cancelling the downlinkleakage signal present on the uplink path.

In block 506, a multi-stage isolation sub-system can attenuate theresidual noise and downlink intermodulation products by combining thesecond cancellation signal with signals received on the uplink channel.For example, the second cancellation signal can be combined with thesignals on the uplink channel using a standard RF coupler device. Thephase of the second cancellation signal can be inverse to the phase ofthe signals representing the residual noise and downlinkintermodulation. Combining the second cancellation signal with thesignals present on the uplink channel can result in attenuating orcanceling any residual noise or intermodulation products on the uplinkchannel.

While the present subject matter has been described in detail withrespect to specific aspects and features thereof, it will be appreciatedthat those skilled in the art, upon attaining an understanding of theforegoing may readily produce alterations to, variations of, andequivalents to such aspects and features. Accordingly, it should beunderstood that the present disclosure has been presented for purposesof example rather than limitation, and does not preclude inclusion ofsuch modifications, variations and/or additions to the present subjectmatter as would be readily apparent to one of ordinary skill in the art.

The invention claimed is:
 1. A multi-stage isolation sub-system,comprising: a first stage device configured to generate a firstcancellation signal for attenuating a downlink leakage signal receivedon an uplink channel, the first cancellation signal comprising aninverse signal characteristic as compared to the downlink leakagesignal; and a second stage device communicatively coupled to the firststage device and configured to generate a second cancellation signal forattenuating residual downlink noise and downlink intermodulationproducts received on the uplink channel.
 2. The multi-stage isolationsub-system of claim 1, further comprising a coupler configured tocombine the first cancellation signal with signals received on theuplink channel.
 3. The multi-stage isolation sub-system of claim 2,wherein the first stage comprises an air interface modeling module; andwherein the second stage comprises a non-linearity modelling module. 4.The multi-stage isolation sub-system of claim 3, wherein the first stagedevice comprises an adaptive filter communicatively coupled to the airinterface modeling module and the second stage device comprises anon-linear equalizer communicatively coupled to the non-linearitymodeling module.
 5. The multi-stage isolation sub-system of claim 4,wherein the air interface modeling module is configured to generate afirst set of parameters using a reference signal and to provide thefirst set of parameters to the adaptive filter, wherein the adaptivefilter is configured to generate the first cancellation signal based onthe first set of parameters, wherein the non-linearity modeling moduleis configured to generate a second set of parameters using the referencesignal and to provide the second set of parameters to the non-linearequalizer, wherein the non-linear equalizer is configured to generatethe second cancellation signal based on the second set of parameters. 6.The multi-stage isolation sub-system of claim 3, wherein the first stagedevice comprises a first non-linear equalizer communicatively coupled tothe air interface modeling module and the second stage device comprisesa second non-linear equalizer communicatively coupled to thenon-linearity modeling module.
 7. The multi-stage isolation sub-systemof claim 6, wherein the air interface modeling module is configured togenerate a first set of parameters using a reference signal and toprovide the first set of parameters to the first non-linear equalizer,wherein the first non-linear equalizer is configured to generate thefirst cancellation signal based on the first set of parameters, whereinthe non-linearity modeling module is configured to generate a second setof parameters using the reference signal and to provide the second setof parameters to the second non-linear equalizer, wherein the secondnon-linear equalizer is configured to generate the second cancellationsignal based on the second set of parameters.
 8. The multi-stageisolation sub-system of claim 7, wherein the first set of parameters andthe second set of parameters comprise information indicating an amountof phase shift to apply to the downlink leakage signal.
 9. Themulti-stage isolation sub-system of claim 2, wherein the first stagedevice comprises a gain/phase control module communicatively coupled toa variable gain unit and a variable phase unit, and the second stagedevice comprises a non-linear equalizer communicatively coupled to anon-linearity modeling module.
 10. The multi-stage isolation sub-systemof claim 9, wherein the gain/phase control module is configured tocontrol phase of the variable phase unit and gain of the variable gainunit, where the variable phase unit and the variable gain unit areconfigured to generate a first cancellation signal; and wherein thenon-linearity modeling module is configured to generate a first set ofparameters using a reference signal and to provide the first set ofparameters to the non-linear equalizer, wherein the second non-linearequalizer is configured to generate the second cancellation signal basedon the second set of parameters.
 11. A method, comprising: generating afirst cancellation signal comprising an inverse signal characteristic ascompared to a downlink leakage signal received on an uplink channel by aradio circuit; generating a second cancellation signal for attenuatingresidual downlink noise and downlink intermodulation products receivedon the uplink channel; attenuating the downlink leakage signal bycombining the first cancellation signal with signals received on theuplink channel; and attenuating the residual downlink noise and downlinkintermodulation products by combining the second cancellation signalwith the signals received on the uplink channel.
 12. The method of claim11, wherein the first cancellation signal is generated by an adaptivefilter and the second cancellation signal is generated by a non-linearequalizer.
 13. The method of claim 11, wherein the first cancellationsignal is generated by a first non-linear equalizer and the secondcancellation signal is generated by a second non-linear equalizer. 14.The method of claim 11, further comprising: generating a first set ofparameters using a reference signal and an air interface model;providing the first set of parameters to a first non-linear equalizer,wherein the first non-linear equalizer generates the first cancellationsignal based on the first set of parameters; generating a second set ofparameters using the reference signal and a non-linearity model; andproviding the second set of parameters to a second non-linear equalizer,wherein the second non-linear equalizer generates the secondcancellation signal based on the second set of parameters.
 15. Themethod of claim 14, wherein the first set of parameters and the secondset of parameters include information indicating a phase shift to applyto the downlink leakage signal.
 16. The method of claim 11, furthercomprising: generating a first set of parameters using a referencesignal and an air interface model; providing the first set of parametersto an adaptive filter, wherein the adaptive filter generates the firstcancellation signal based on the first set of parameters; generating asecond set of parameters using the reference signal and a non-linearitymodel; and providing the second set of parameters to the a non-linearequalizer, wherein the non-linear equalizer generates the secondcancellation signal based on the second set of parameters.
 17. Themethod of claim 11, wherein the second cancellation signal is generatedby a non-linear equalizer and the first cancellation signal is generatedby a variable gain unit and a variable phase unit.
 18. A remote antennaunit, comprising: a multi-stage isolation sub-system communicativelycoupled to an uplink antenna and a downlink antenna, the multi-stageisolation sub-system comprising: a first stage device configured togenerate a first cancellation signal to attenuate a downlink leakagesignal received at the uplink antenna, the first cancellation signalcomprising an inverse signal characteristic as compared to the downlinkleakage signal received at the uplink antenna; and a second stagedevice, communicatively coupled to the first stage device, the secondstage device configured to generate a second cancellation signal toattenuate residual downlink noise and downlink intermodulation productsreceived at the uplink antenna.
 19. The remote antenna unit of claim 18,wherein the multi-stage isolation sub-system further comprises acoupler, communicatively coupled to the first stage device, the couplerconfigured to combine the first cancellation signal with signalsreceived on the uplink antenna.
 20. The remote antenna unit of claim 19,wherein the first stage device comprises an adaptive filter configuredto generate the first cancellation signal and the second stage devicecomprises a non-linear equalizer configured to generate the secondcancellation signal.
 21. The remote antenna unit of claim 19, whereinthe first stage device comprises a first non-linear equalizer configuredto generate the first cancellation signal and the second stage devicecomprises a second non-linear equalizer configured to generate thesecond cancellation signal.
 22. The remote antenna unit of claim 21,further comprising: an air interface modeling module communicativelycoupled to the first non-linear equalizer, wherein the air interfacemodeling module is configured to generate a first set of parametersusing a reference signal and provide the first set of parameters to thefirst non-linear equalizer, wherein the first non-linear equalizer isconfigured to generate the first cancellation signal based on the firstset of parameters, an non-linearity modeling module configured togenerate a second set of parameters using the reference signal andprovide the second set of parameters to the second non-linear equalizer,wherein the second non-linear equalizer is configured to generate thesecond cancellation signal based on the second set of parameters. 23.The remote antenna unit of claim 22 wherein the first set of parametersand the second set of parameters comprise information indicating anamount of phase shift to apply to the downlink leakage signal.
 24. Theremote antenna unit of claim 18, wherein the first stage devicecomprises a gain and phase controller configured to generate the firstcancellation signal and the second stage device comprises a non-linearequalizer configured to generate the second cancellation signal.